Apparatus for forming hollows in spherical fuel elements



L. RACHOR A ril 23, 1968 APPARATUS FOR FORMING HOLLOWS IN SPHERICAL FUELELEMENTS Original Filed Sept. 4, 1964 IN VEN TOR.

zor/l/l/P 1966/7019 United States Patent 3,379,076 APPARATUS FOR FORMINGHOLLOWS IN SPHERICAL FUEL ELEMENTS Lothar Rachor, Kleinauheim (Main),Germany, assignor to Nulrem Nuklear-Chemie nnd -Metallurgie Gesellschaftrn.b.H., Wolfgang, near Hanan (Main), Germany Original application Sept.4, 1964, Ser. No. 394,404, new Patent No. 3,284,314. Divided and thisapplication Jan. 26, 1966, Ser. No. 523,172 Claims priority, applicationGermany, Sept. 13, 1963, N 23,747 3 Claims. (Cl. 77-3) ABSTRACT OF THEDISCLOSURE A device for forming spherical hollows in nuclear fuelelements consists of a part mounted for movement in two straight-lineguides at angles to each other and a chisel with a curved edge ismounted by one end on said memher to move in an are such that it cuts aspherical hole in the sphere as the sphere is rotated about its axis.

This application is a division of application Ser. No. 394,404, filedSep. 4, 1964 and now Patent No. 3,284,314.

The earlier application describes in detail a fuel material for nuclearreactors composed of hollow spheres which consists of a body ofelectro-graphite of good heat conductivity and mechanical strength whichmay be closed by plugs, which can be screwed in. A hollow is formed bythe shell, which is preferably spherical or nearly spherical. Thenuclear fuel material of the mixture of nuclear and breeder material ispositioned in the hollow in a relatively thin layer on its wall.

The present invention relates to an apparatus for use in making suchspheres which is fast, inexpensive and simple.

Further objects and advantages of the invention will appear more fullyfrom the following description, especially when taken in conjunctionwith the accompanying drawings which form a part thereof.

In the drawings:

FIG. 1 shows in cross-section a sphere of the type to be produced;

FIG. 2 shows a machine embodying the invention; and

FIG. 3 is a geometrical diagram for explanatory purposes.

The shell 1 to be produced is formed of graphite and has a centralhollow, on the inner wall of which is formed a layer 3 in which the fuelmaterial, advantageously in the form of coated particles, and preferablymixed with graphite, is embedded.

The outer diameter of a sphere is, for example, 60 mm. and the diameterof the hollow is 36 mm., whereas the coated particles have a diameter ofabout 0.4 to 0.7 mm. and are covered with a coating about 0.1 mm. thickof a material impervious to gases.

The shell has a filling opening which is closed by a plug 2. Thecross-section of the filling opening in which the plug 2 is secured issubstantially smaller than a crosssection of the hollow.

The head of the plug which closes the filling opening is of conicalshape, the length of the conical part being desirably from 30% to 50% ofthe length ofthe plug.

FIG. 2 shows an arrangement which is well adapted to produce on aturning machine such fuel elements, particularly for the formation inthe sphere of a hollow.

The arrangement includes a chisel with a rounded point 4a by which apart of the inner contour of the hollow is formed through movement ofthe point in a circular arc, the radius of which corresponds with thatof the hollow, while the remainder of the end portion of the work toolis constituted by a circularly profiled cutting edge. The workingmovement of the chisel generally consists of a movement around a pointin the area of the filling opening of the ball, which can be quite smallif the tool is of sufficient rigidity.

Referring again to FIG. 2, a chisel 4 is fastened on and spaced above acarrier part 5. This carries a guiding groove 6 and a bolt 7. It iscarried by a base 8 with a guiding bolt 9 and a guiding groove 10.

The carrier part is turnable about the bolt 9 engaged in guide 6, whilebolt 7 slides in the groove 10. The carrier 5 is suitably secured to thebase plate 8.

The chisel includes a further edge 17 at an angle to its longitudinalaxes.

The swinging of the carrier 5 is limited by stops 11 and 12.

In operation, a cylindrical bore is first formed in the shell 1 asindicated by dotted lines at 18. With the bolt 7 in the bottom of theslot 10, the carrier 8 is moved forwards (to the left in FIG. 2) untilit engages stop 14, so that the chisel enters the bore 18. The ball 1 isthen totated by a suitable mechanism around the axis of the bore 18, andcarrier 5 is gradually shifted counter-clockwise.

During a part of the movement, the tip of the chisel swings in thecircular are 15 and thereafter the chisel is withdrawn longitudinally sothat the edge 16 forms the remainder of the spherical interior. The edge17 follows the contour of the filling opening.

FIGURE 3 shows the geometrical basis of this movement. A turning of thestraight line g about the point D only would result in the ark k. Forachieving the arc k around the center K of the sphere, a longitudinaldisplacement of the straight line G by the amount a is necessary. Thislongitudinal movement is made possible in a very simple way by guiding asuitable point of the straight line g in a straight line S perpendicularto the line DK at a suitable distance from D. The distance a, on thestraight line g between the secant s and the arc k corresponds withsuflicient exactness to the distance a between the areas k and k While Ihave described herein one embodiment of my invention, I wish it to beunderstood that I do not intend to limit myself thereby except withinthe scope of the claims hereto or hereinafter appended.

I claim:

1. Apparatus for producing a fuel element composed of a hollow spherehaving a filling opening, comprising a chisel having a cutting edgeincluding a rounded tip, and means mounting said chisel for simultaneousrocking and longitudinal movement to cause said tip during part of suchmovement to move in an arc having a radius equal to the radius of thehollow, said tip having its cutting edge curved about an axisperpendicular to the direction of such longitudinal movement, and saidchisel being supported by said mounting means only at the end remotefrom said tip.

2. In a claim as claimed in claim 1, said chisel edge having a sectionadjacent to the tip curved about a radius equal to the radius of thehollow.

3. In a claim as claimed in claim 1, said mounting means including twostraight-line guides.

References Cited UNITED STATES PATENTS 2,403,668 7/ 1946 Maddock 82-112,431,815 12/1947 Linn 82-11 2,821,813 2/1958 Degler 82-11 3,120,7232/1964 Jessup 82-11 GERALD A. DOST,Primary Examiner.

